generator/welder issue.

[mhooker32]

miller generator/welder. at 1800 rpm, the generator portion should output 60 hz, 120v. . its 4 pole. output is 65v at 40 hz.. will output 60hz and 120v at about 3400 rpm. . the welder portion is a separate stator, it also outputs half the voltage and HZ. i suspected a bad pole on the rotor,. as a half assed test, i applied 12v to the slip rings. inserting a thin welding rod at each pole showed the same magnentic attraction. i was expecting a dead pole. . ohms out at 18 ohms, which is correct. on the 240 volt plug, i get read 60 v, 40hz from one leg to neutral or ground, . 120v and 40hz from hot to hot. . . runs like a 2 pole unit. im really stuck . . i ran it at 3400, and i get 60hz, but thats way to high rpm. for a moment, i saw the fluke spike to 130hz, but when i set it to min max it didnt do it again. . i can send a schematic. the fact that it has a generator stator and a welder stator that has the same issue makes me think its somehow the rotor. if it is, its a goner. i hope not. it spent a lot of time getting it to run like a top, now this. any thoughts?

[MEXICOWANDERER]

Yes I always assume a poster has done his homework before posting. Having had to diagnose issues with 12 pole 600 RPM machines nothing can be left to chance. Early Onans with saturated field (volts per Hz) and Delco RR Detroit volts per Hz machines called for careful and methodical troubleshooting.
Thank you OP !!!

[2112]

I see I'm late to this party but for generator questions some people on This Forum are very knowledgeable.

[mhooker32]

two slip rings on both the 2 and 4 pole rotors.

thanks

[theoldwizard1]

mhooker32 wrote:
He later emailed me a spec sheet of rotor readings, etc., and confirmed in the email it was a 2 pole rotor.

So are there 2 pair (total 4) slip rings/brushes ?

Some, not all, standard non-inverter generator have automatic voltage regulator that adjust rotor voltage to get the correct output voltage. THIS DOES NOT affect frequency ! Frequency is strictly controlled by the engine speed.

So if you are tweaking a non-inverter generator, set your governed engine speed so that you get about 61 Hz unloaded and greater than 58 Hz under near full load. The regulator has an adjustment screw for output voltage. You have to compromise between unloaded and loaded. You are shooting for 120VAC +/-10%.

In general, stay away from brushless generators especially if you are planning on running electronics. They have very high total harmonic distortion.

[enblethen]

Thanks for your update!

[mhooker32]

ok, i wasted a lot of your time with bad info. i feel i didnt waste my time, as i learned a ton of **** about generators . bottom line, i was operating on bad information. i had written to miller with some questions on how the machine operated. i gave them the serial #. i was told it generates 120/240v power at "idle" 2000 rpm. then you kicked it up to 3600 rpm to get 80v ac open voltage at the cables. mine didnt. i dug thru various roughneck and the later blue star schematics. it turns out my unit is a 2 pole rotor, and will only get to 60HZ running at 3600 rpm. the blue star, and earlier roughnecks have a 4 pole rotor. i say that because there are youtube videos of roughnecks with multiple cable jacks for various voltages. in the video , those did 60 hz at 2000 ( idle). additionally confusing, what engine idles at 2000? anyway, mine has the big selector. my friend has a blue star 2E and i went there today. i could clearly see inside a 4 pole rotor. all the miller diagrams i looked at show a generic field drawing, no mention of poles. now looking thru the parts diagrams, you can see a 4 pole rotor in the early roughneck 2e, a 2 pole rotor in my later 2e, then back to 4 pole in the blue stars. ps- why the hell would they downgrade from a 4 pole to a 2 pole? at 3600 rpm, this motor is screaming. i would not use it as a generator in a blackout unless i really had no choice. anyway, i set it up to run full at 3600, and open welding voltage is good, 120/240 output is good. quite frankly, if i knew it was 2 pole, i might have passed on it. still , i paid 150 bucks for it, 200 for a new ignition system, so no real complaints. ps- i spoke a miller guy, and told him there was no way my unit had a 4 pole rotor in it, even if he said it did. he later emailed me a spec sheet of rotor readings, etc., and confirmed in the email it was a 2 pole rotor. i was scared ****less that i has some kind of frequency loss due to a bad rotor, and running it to 60HZ would blow it apart. i ended up buying an optical rpm tester, and it confirms 3600 rpm at 60 hz. . when its running it sounds like 36,000 , the sucker is really cranking. anyone with any questions about these things, let me know. i know it inside out now.

thanks to all

[Trackrig]

Not asked, but answered anyways..........

Bill

[MEXICOWANDERER]

Me...

[theoldwizard1]

MEXICOWANDERER wrote:
One of 3 phases open on the secondary stator winding will also affect Hz

Who said anything about 3 phase ?

[theoldwizard1]

Any split phase generator should have the same resistance from the output leg to neutral. If not, you have a bad stator. If there are only 2 brushes, then there is only one rotor field.

Remove and inspect brushes. Clean slip ring.

Unless it is an inverter generator, the frequency is controlled by engine RPM. It is NOT a coincidence that 60 Hz generators run at either 1800 or 3600 RPM (multiples of 60).

[MEXICOWANDERER]

One of 3 phases open on the secondary stator winding will also affect Hz

[enblethen]

May want to read through this:
Miller troubleshooting

[mhooker32]

ok. just looked at it. inserted thru the back a long 1/4 inch steel rod into the opening between a pole and the stator. with 12v on the brushes, you cant even pull out the rod. disconnect the 12v and the rod releases. it does the exact same thing on all 4 poles, equally. i think that rules out the rotor. i ran the machine at 2200 rpm with 12v on the brushes. 39-40 hz, about 30v ac . with the power to the slip rings disconnected, i still get 39-40 hz just from the residual magnetism, but of course very low AC, 1.5 volts. put back to normal with a new bridge rectifier brings me back to the orig problem, 39-40 hz, 70 volts AC at 2200 rpm. should be over 60hz and 120v. what else could it be? the stator is two windings with a center tap. both X and w outputs on the stator exhibit the same condition. you see the same acrosss X and Y. which are the hot legs for 220 v. there i ger the same 40 Hz, and around 120v. WTF could it be?

[mhooker32]

rectifier tests good. i also disconnected the bridge and ran pure 12v straight from the battery to the brush holder. still low HZ. at the same rpm, the output voltage would be reduced with only 12v, but the HZ should still be 60